Propane fractionation of reduced crude oil with recycle of a solvent extract



stituents.

Patented ct. 2, 1951 2,570,044 ICE PROPANE FRACTIONATION F REDUCED CRUDE OIL WITH RECYCLE 0F A SQL- VENT EXTRACT Bruce C. Benedict and William N. Axe, Bartlesville, Okla., assignors to Phillips Petroleum Company, a corporation of Delaware Application December 23, 1948, serial Nb. 66,991

7 Claims. 1

This invention relates to propane-fractionation of lubricating oil stocks. In one of its more specific aspects it relates to a method for the treatment of low asphalt-containing lubricating oil stocks for the separation and recovery of lubricating oil fractions. In a still more specific aspect it relates to a process for the separation and recovery of lubricating oil fractions from crude lubricating oil stocks containing asphaltic constituents by treatment with liquid propane wherein the asphaltic constituents are not precipitated and caked in oil fractionating apparatus.

Deasphaltng petroleum oils and more particularly reduced crude oils from which distillate lubricating oil fractions have been removed is old in the art. Such operations are usually car-` ried out at temperatures between about 70 and 140 F. to take advantage of the precipitating action of propane on the heavy asphaltic constituents of the oil. It has also been recognized for many years that a fractionating effect can be obtained with propane-oil mixtures at temperatures ranging from about 140 F. up to the critical of propane. Utilizing the unique properties of liquid propane whereby increasing temperatures result in progressive rejection of hydrocarbons in such a manner that the higher molecular weight components and the more aromatic and napthenic components are separated first and the lighter components and more parafnic hydrocarbons last, a combination of low temperature distillation land solvent extraction is achieved. However, due to the diinculties involved in working at high pressures and in close proximity to the critical temperature of propane, commercial exploitation was unknown until quite recently.

It has been found, however, that some lowasphalt content reduced crude lubricating oil stocks may be fractionated continuously for long Iperiods of time by liquid propane at high temperatures and under correspondingly high preseures, while other low-asphalt crude lubricating oil stocks can be fractionated for only short periods of time. In these latter cases it has been found that the contacting equipment became plugged with hard deposits of asphaltic material. These asphaltic materials had apparently been precipitated from the oil upon contact with the high temperature liquid propane. It should be mentioned that all the oils in question were lowasphalt content oils and did not differ significantly from each other in total content, as conventionally determined. Why certain of these oils caused plugging and others 4did not is not clearly understood.

An object of our invention is to devise a process in which a low-asphalt-containing reduced crude lubricating oil stock is fractionated for the separation and recovery of lubricating oil con- Another object of our invention is to devise a method for the separation and recovery of lubricating oil fractions from such crude oil stocks by fractionation with liquid propane without the formation of hard asphaltic deposits in the oil fractionation apparatus. Still another. object of our invention is to devise a continuous process for the separation and removal of lubricating oil fractions from low asphalt-containing reduced crude oil stocks suitable for the manufacture of lubricating oils by fractionation with propane wherein the asphaltic. naphthenic and aromatic oil constituents are stripped of some of their higher Viscosity index oily constituents in such a manner that a hard mass does not deposit in the extraction equipment. Still other objects and advantages of our invention will be obvious to those skilled in the art upon reading the following disclosure, which, taken with the attached drawing, forms a part of this specification.

In preparing to apply the above mentioned unique properties of liquid propane to actual commercial separation of certain grades of lubrieating oil from residual stocks, a hitherto unrecognized problem Was encountered. Upon treating some Mid-Continent reduced crude oil stocks with liquid propane in a countercurrent contacting tower at a propane-to-oil volume ratio of about I7:1 with temperatures ranging from about F. at the top to about 175 F. at the bottom of the tower an SAE 40 oil was separated in the overhead product. On the other hand, when a very similar Mid-Continent reduced crude oil stock was charged to the process under the same operating conditions a similar fraction of lubricating oil was initially obtained., but the column rapidly filled with a hard asphaltic material in the stripping section, thereby making continuous operation impossible. In this second case, the formation of a third phase, that is, a semi-fluid asphaltic phase was produced along with a propane-rich light oil phase and an oilrich phase of propane in heavy oil. Upon contacting the charge oil with liquid propane this third phase when first formed was sufficiently Huid to flow nearly to the bottom of the column before the ascending propane had washed it suiiiciently to cause it to set to a hard cake. Upon continued operation this cake builds up in the lcolumn until complete closure of the column occurs. Why one low asphalt-containing oil should deposit its asphalt while another low asphalt-containing oil does not when the two oils contain similar amounts of asphalt is not delinitely known. i

In a study of three Well known Mid-Continent reduced crude oils which have 'been long recognized as excellent sources of lubricating oil `stocks hard deposits were formed when treating two of these stocks with liquid propane while the third was fractionated with propane continuously and without difficulty. It has also been found that some West Texas' reduced crude. oils can be frac'-Y realized that propane fractionatioin cannot beA universally applied to all so-calledV low-asphalt content reduced crude lubricating oil stocks.

We have discovered thatthe addition of aromatic and naphthenic extract oils,` such as may be obtained from most any solvent extraction process, to the reduced tionation column serves to modify theoil' characteristics in such a manner phase is not deposited in the propane solution. We have found further that by adding suchk extrac-tolls to the 'feedstock to the propane column or tothe feed' plate of the column that the overall yield.Y ofV high V. I. components is increased since some high V; I. components ordinarily l'ost in an extractioin operation are recovered by our process. We have also found that in the propane fractionation of reduced. crudeY oil stocks by ourl process for the production of such an oil as SAE 50 as overhead product the asphaltecontainng bottoms'may be further 'fractionated' to produce an SAE 70 or 250 overhead oil', while bottoms from this last vfractionation step maybe still further fractionated. The aromatic and naphthenic extract oils may traction column at or near the feed point.

i The gureshows diagrammatically and in ele- :i

vation one form of apparatus in which the process ofV our invention may be practiced;

The apparatus consists essentially of three main parts. The rst part is a propane fractionation section consisting ofcolumns'Z and I6; The secondpart consists Vof a solvent extraction systemY having a main extraction column 8 and a stripper column I2. The third portion is a more or less auxiliary. portion of the apparatus 'and consists of a solvent extraction system having an extraction column 32 and a stripper 3'6.

Broadly speaking,A our process consists in charging a reduced crude lubricating oil stock to the propane column 2- which has been previously filled with liquid propane Vunder pressure. A slution of oilin propane leaves the top of' this column through a line Land p asses into a strip'- per column 5' at aboutits mid-section. The botitoms 23 which is an oil-rich phase' containing some dissolved propaneV are removed' from the propane column rthrough a line 2l to the second propane fractionation column' I6.. From this col'- umn a solution of oil in propane is removed from thetop by way of a line I'I to recoveryV apparatus, not shown, for separating the oily Aconstituents from the propane. containing some dissolved.4 propane accumulates in the bottom of vessel. I6. This phase may be withdrawn through a line.Y I8 to a stripping vessel, not shown,Y for the separation of' the propane from the asphaltic and other heavy oily constituents. Reference numeral 24 indicates the liquid-liquid interface between the upper propane Solution containing dissolved oil and the lower oil rich phase containing some dissolved propane. Additional propane for this fractionation step is introduced through a line I9' into the oil rich phase 25.` f

The interfacer indicated by reference numeral' 22 separates the propane" solutionY of oil' from the oil-rich phase in the primary fractionator 2. Propane for fractionation inl this column is added through a line 3 directly into the oil-rich phase 23. Aline IA is provided for introduction of,V the reduced crude oil feed' stock into column 2. Line I is also provided for introduction ofthe crude crude` oil feed to a fracl that a hard third be introduced into the exy An. oil' rich phase' CTL oil feed stock into thiscolumn in case it is dei sired to mix somesubsequently produced recycle stock with the feed charge prior to introduction of. the latter. intothe column. The propane introduced intothe oil phase 23 through line 3 and into-'the oil phase 25 through line I9 is introduced thereinto by some distribution means, not shown. VVGrood contact between rising propane globules and the heavy oil phase is intended so that the propane on reaching the interface 22 Ortheinterace 25a. is saturated or substantially saturated with propane-soluble oily constituents remaining in the oil-richrphase.

The stripper column 5' may be referred to as a depropanizer column since, its function4 is' pri-7 marily forr the separation of propane from the oily constituentsy taken` overhead through pipe# from' fractionator 2'.' Theseparatedl propane leaves this depropanizer through anoverheadline G'and' maybe passedv to a run storage.. no tshown; prior torecyrclingl tothe system. The propanefree oil' is removed from the vessel' 5` through a; line l andY passed' into the lower` portion of the extraction column 8. Into` the top of thiscolumn through a line 9 isY added an extraction solvent", for example', phenol. The oil from line4 'I` and the phenol from line 9 are countercurrently contacted in this column andthe rafnate-remaining after extractionY is'removed through an overhead line la to separation equipment, not shown'. Aline 2U is provided near the lowerV end of column E; for introduction of some water incase a refluxing action in this part ofthe column i's desired: The extract phase isA removed through a line' I-I' and transferred to the stripper column I2- in4 which phenol is separatedV from the extract oil. From this separator the phenolA may be transferred through a line I3Y to a run storage vessel.. not shown; while the extract oil isv removed' through a line I4 for passage to storage,not shown; or passage through a line I5 for cyclingwith' the reduced` crude oil charge stockinto theK primary propane fractionator r2;

vThe system of'vessels 32 and 36" is provided for use when additional extract oil over that provided from vessel' I2' is required' for recyclingV into the primary fractionator 2; is introduced through a line 33' into thel topfof the column while an oilto'be extracted' is'intro'- duced through a line 31| ata' point near the bot'- tom of the column. Rafnate' oil isv removed through a line 34 at the top while the extract oil is removed' through a line 35' from thebottom of this column and transferred into, the stripper column 3B at about amidj-point; VThe stripped or recovered phenol is removed from this latter co1'- umn through aline3l`and1may be passed to store age, not shown, or recycled, directly into thev ex'- traction column 32`throughpipe 33: The extract oil accumulating in the bottom ofthe stripper 3,6 is removedthrough a line 38; and all or aporti'on thereof may be passed' throughl a line 3'9 andl'lin'e 4G' for introduction into the' stream of extractoil flowing in pipe I5 for charging to the main progpane. fractionator 2'. That portion of' oil. from the bottom oi'vessel 3B' not needed for recycling may be passed on through line 38' for such disfposal as desired. The pipe 4U' is shown in the drawing asa dotted line since under.` some conditions the oil from vessel' 36' may notV be used` in the system` and in this case vesse1s32`and-36 are not needed'.

Ving point is preparedin apparatus, not shown; by

In column 32 phenol is discharged through line distillation of a Mid-Continent crude oil to remove the SAE and 20 stocks. This reduced crude oil stock then contains all crude components heavier than the SAE 20 oil and it is then fractionated in the propane columns to produce SAE 50 and 70 oils as overhead products and a final oil-asphalt bottom product according to the following sequence of operations.

The reduced crude is charged into the propane column 2 through the line I. This column, of course, is previously filled with liquid propane through line 3 and the column is maintained at a pressure of about 640 pounds per square inch gauge. The crude oil feed plate or ring is positioned at approximately midway between the top and bottom of the column or midway between the interface 22 and the top of the column. The temperature at the feed plate is maintained at (about 185 F. During operation propane at about 175 F. is pumped into the column at the above mentioned pressure through line 3 at a rate such that the volume ratio of charged propane to oil feed is between 7:1 and 8:1. The ascending propane serves to strip the downiiowing oil not dissolved by the propane solution at the feed plate while the fractionating section above the feed plate tends to precipitate the higher molecular weight and the more aromatic components from the propane-oil solution on account of the temperature gradient through the upper section of the column which ranges from about 185 at the feed plate to about 195 F. at the top. For maintenance of this relatively high top column temperature a heating coil 42 is provided.

The ov-erhead product removed from column 2 is composed of a propane solution of SAE 40 to SAE 50 oil depending upon the particular operating conditions. The bottoms product from this column consists of the heavier lube oil components and the asphaltic components and is continuously removed through line 2| and charged into column IB at a mid-point. In this column conditions of temperature, pressure and propaneto-oil ratio are so adjusted as to fractionate the feed into an SAE 70 or an SAE 250 stock which leaves this column through the line I1 as a propane solution. The asphaltic bottoms containing still some oily material and propane in solution I8 to such propane stripping and disposal as desired. In case an SAE 70 oil is taken overhead from column I6 and it is `desired to produce also an SAE 250 oil, the bottoms oil from line I8 may then 'be passed into a third propane fractionator column similar to column I 6. In this third column, then, the operating conditions will be maintained such that the 250 SAE oil will pass overhead in solution in propane and the asphaltic and still heavier oily material may be discharged from the bottom for still further treatment or for such disposal as desired. In both columns 2 and I6 the interface between the propane solutions of oil and the oilrich phases are maintained at relatively low levels so that the main bodies of propane may have ample opportunity to extract soluble constituents from the oils charged to these two columns. However, these interfaces are sufliciently higher than the points of propane addition that by the time the propane reaches the interface itis almost saturated with soluble constituents from the respective oil-rich phases. The overhead stream of oil in propane from column 2 passes through the line 4 into the depropanizer column 5 in which the propane is separated from the oil. `The separated propane is passed througha line 6 6 to storage or may be condensed and passed directly to the propane inlet line 3. It is preferable, however, to use a run storage tank. The extract oil recovered in the depropanizer 5 is passed through the line I into the lower portion of the solvent extraction column 8. The column 8 has. of course, been previously iilled with solvent which in this example is phenol. During continuous operation phenol is fed into the column through line 9 at such a rate so as to maintain an overall phenol-to-oil ratio of from 1:1 to 4:1 depending upon the extent of extraction desired. A temperature gradient of about 20 is maintained in this column ranging from about 200 F. at the top to about 180 F. at the bottom. If a reluxing action is desired to alter the solubility relationships of the oil in the phenol near the point of removal of extract some water may be added through the line 20 into the bottom of the column 8. Approximately 10 per cent of Water based on the volume of phenol charged may be added. The volume of water may, of course, be varied as desired depending upon the extent of reiluxing desired. The ralinate phase of oil containing some phenol is removed from this column through the line I0 for further iinishing operations while the phenol-rich extract phase is discharged through line I I into the stripper I2 in which the phenol and the extract oil are separated. The phenol is passed through a line I3 to a run storage tank, not shown, prior to recycling into the extraction colunm 8. The extract oil is removed from the bottom of the stripper I2 through the line I4 and is passed through the line I5 into line I in which crude oil charge stock is Iiowing. In line I the crude oil charge stock and the extract oil from line I5 are mixed and the mixture then is introduced as charge oil into the primary propane fractionator 2. In case the volume of extract oil from line I4 is larger than necessary for recycling purposes the excess may be passed on through the line I4 to a storage tank, not shown, for such disposal as desired. In this method of operating wherein the extract oil is mixed with the charge oil in line I a hard asphaltic deposit is no-t formed in the lower portion of the propane fractionator 2.

The phenol free extract oil recovered from the Amatic (low V. I.) components are ultimately discharged from the system in the asphaltic product through line I8 While the high viscosity index components are recovered as components of the overhead products from columns 8 and I6.

An optional method of operation of the present process involves the use of additional solvent extraction equipment in such a way that advantage may be taken of distillate extract oils from SAE l0 and SAE 20 oils which because of their high aromaticity are unusually useful in preventing the depositing of asphalt in the propane fractionator. This auxiliary system does not alter in any manner the previously given processing of material but it is supplementary in that the extract oil from the SAE 10 and 20 oils is blended 7 iiitlittheffheayierextract oill from the stripper v-I2 and this mixture is then lmixed with the raw charge. offreduced crude oil, This operation then assists further -in preventing the precipitation andvdepositionof the-hard asphalt in the propane fractionator 2 in addition to increasing the yieldof high viscosity index material.

lnV the operation of this auxiliary equipment which is essentially an extraction column'32 and theV stripper 356 theraw SAE. 10 and 2()V distillate mixturewhich was previously separated by distillation fromy the reduced crude oil charge prior to :passage ofthe latter stock into the propane fractionator?, is charged to the phenol extraction column 32 through 1ine-3 i. Sufcient phenol -is introduced into the column through the line `33 to .maintain a phenol-to-oil ratio Yof from about 1`: Ill-to 3:1. A temperature gradient of from about 175 `at the top o the column to about 155 att-he bottom is maintained in this contacting vessel. The higher top tower temperature is rmaintained by passage of a heating medium through a Vheating coil e3. 1f additional reuxing offthefextract phase is desired, some watermay be-'added to the bottom of the extraction vessel .through a line l. The amount of this water addedfmay vary from-a trace up to about l per cent by volumegbased on the amount of phenol added ,topline 33. Theraffinate oil from this extractor fpassesthrough the overhead line 34 to a phenol recovery stripper Vessel, not shown, from which .ftheoil may pass to a storage vessel, not shown, while-the recovered phenol may pass to a run storage, also not shown, prior to recycling th-rough line 33 into this extractor. The extract phase `is-passed from the bottom of this vessel throughv .the line 35 `into the stripperii in which the phenol, Vwater Vand oil are separated. The :phenol and .water may be withdrawn from the stripper through line 3'! to further sepa-ration apparatus inA which the water and phenol may be separated while the extract oil is withdrawn through the'line 36. All or a portion of this extract oil may be recirculated through the line 33 and line iii into line `i5 for admixture with the raw crude .oil cha-rgewin -lineprior :to passage into th-e primary propane fractionator 2. Itmore extract-pills produced in column 36 than is `nec- ;essary for recycling into column 2 for the prevention-ofthe asphalt deposits the excess oil may be .passed on .through line 38 to a storage or to other :processing ordisposal as desired. However, by `passing ex-tractoil from the stripper,l 36 into the .primary fractionator 2 -the yield of high viscosity oils from lthe process Vis increased and according- .ly it is usually desired for lthis reason to pass the entire-amountof extract oil from stripper 3S into .column 2. The addition of more aromatic and vnaphthenicoil -to the raw crude oil'charge stock vthan is necessary to just prevent the deposition of hard asphalt does not in any way hinder the yoperation of our process. More extract oil than just required to cause asphalt to just not deposit will merely cause the asphalt accumulating Ain -the bottom of the propane extractor to be .-somewhat more fluid than it would otherwise be.

The amountof extract oil froml the stripper YIZ-When producing an SAE 50 high viscosity index stock as a rainiate from extraction vessel will usually range from about 3 to lO'per cent of ...the original reduced crude oil charged tothe pro- ;panefractionator 2.

Iny the 4modified process in which extract loils fromthe extraction4 columns 8 and' 32 are-comffbined'ffor recycling thereis frequently availableA -asmuchzasz to 25,-percentfbyfvo1ume rif-extra@ Voil based` on the-crude oil charge.

lngthis; process ,itrhas been found that the quan;

are recovered .invtheroil fractions and the overall kyield of.v high viscosity index oil is' increased.

In vthe drawing the 4aromatic and na-phthenic oil added to theextraction column 2 is shownlas mixed VWith lthe feed stocks and the mixture then introduced into-the` column. The varomaticand -naphthenic oil stream need not be .mixed with the charge oil, as-mentioned hereinbefore, but

-may be introducedibyzitself, into` the column. "It

should preferably be introduced ata point near the feed point, and :not more than 5 ltrays or contacting stages above or below the feed point,'and preferably at the feed point. Y

While the process of the present invention has been described-with phenol-.as the example of the extraction solvent employed, it is to be understood that any extractionl solvent maybe used providing, of course, 'that the solvent will produce a sulcient quantity of highly aromatic and `naphthenic oils for `recycling for the prevention of .theasphaltic deposits.

To maintain uniform or controlled temperature gradients over the vlength of the fractionaftorsf2 and IEand in extractors 3 and 32 it may `be desirable to employ a series of heat exchange coils through the length of these vessels. Such :heaters are not shownv herein for purposes of simplicity since installations andoperations-of such .heat exchange 4equipment are well known to those skilled-in the art.

Contacting trays or Vbaiiles or-other apparatus :may be usedin the propane Viractionators Zand lr6 for lpromoting efcient contact between the Apropane .and oil. These fractionators, however, .may be operated without any packing but ciciency of contacting is not ordinarily very high and it is preferred to use some type of packing apparatus in these towers. Since our process provides a-method of operation in which theasphaltic material does not adhere to the packing within tower 2 anytype of packing desired may be used and ofcourse it is usually desirable to employ Ythatpacking- Vwhich-'Will promote most-efficient contacting between the several liquid phases. Likewise any-.desired type of liquid-liquid contacting equipment may be used in extraction vessels 8 and 32. vSuch liquid-liquid contacting equipment is readily available on the market and .itsfinstallation and use lis well understood by those. skilled .in the art. No special equipment is required' for our process other than the tanks .andpipes, etc., should besuniciently strongto .withstand high operating pressures, such'as the z'lofpounds .pressure mentioned in relation to the {operation-of the -ra'ctionator 2. Pressures in the ,extractionfvesselsg and 32 may be atmospheric VQnslightIy.:higher than atmospheric since there is present in these vessels no highly volatile material like propane.

It will be understood by those skilled in the art that many variations and alterations in the operating conditions of our process may be made without departing from the intended spirit and scope of our invention.

Having described our invention we claim:

1. In the process for .separating and recovering a lubricating oil fraction from a low asphaltcontent crude lubricating oil stock with propane wherein a hard deposit of asphalt is formed and adheres to and plugs the oil fractionating apparatus, a method for continuously carrying out said fractionating operation without plugging of said apparatus by deposited asphalt comprising maintaining a body of liquid propane in a contacting zone, introducing said oil into said zone at a midpoint, introducing liquid propane into said zone at a point near the bottom thereof, withdrawing propane containing dissolved oil from the top and withdrawing an oil-rich liquid phase free from precipitated asphalt from the bottom of said zone; separating the oil from the propane containing said dissolved oil; maintaining a body of phenol in a second contacting zone, introducing the separated oil into said body of phenol at a point near the bottom and introducing phenol at a point near the top thereof, removing a rafnate phase from the top and an extract phase from the bottom of said second zone, separating a mixture of aromatic and naphthenic oils from said extract phase and introducing the separated mixture of aromatic and naphthenic oils free from phenol into said body of propane at the point of introduction of said low asphaltcontent crude lubricating oil stock.

2. In the process for separating and recovering a lubricating oil fraction from a low asphalt content lubricating oil stock with propane wherein -x a hard deposit of asphalt is formed and adheres to and plugs the oil fractionating apparatus, a method for continuously carrying out said fractionating operation Without plugging of said apparatus by deposited asphalt comprising contacting liquid propane and said oil stock in a contacting zone, removing an oil rich phase and a propane rich phase from said zone, separating oil from said propane rich phase, admixing the separated oil and a quantity of phenol, from this admixture removing an extract phase and a rafiinate phase, separating a mixture of aromatic and naphthenic oils from the phenol of said extract phase and returning the separated mixture of oils free from phenol with said low asphalt content lubricating oil stock into the first mentioned contacting step; further treating said oil rich phase from the rst mentioned contacting step with liquid propane, from this admixture separating a propane rich phase and an oil rich phase, recovering asphalt as one product of the process from this latter oil rich phase, and recovering a raiinate oil from said raifmate phase as the second product of the process.

3. In the fractionation of low asphalt content crude lubricating oil stocks with propane wherein a deposit of asphaltic material is formed and adheres to and plugs the contacting apparatus, a process for carrying out said fractionating operation without plugging of said apparatus by deposited asphalt and maintaining the asphalt in solution comprising maintaining a body of liquid propane in a contacting zone, introducing said low asphalt content crude lubricating oil stock 10 into said body of propane at the midpoint thereof, introducing a mixture consisting of naphthenic and aromatic oils into said body of propane at said midpoint, removing propane containing dissolved oil from the top of said zone and recovering the oil therefrom as one product of the process, removing an oil-rich phase containing the asphalt in solution from the bottom of said Zone and recovering the asphalt from said oilrich phase as the second product of the process.

4. The process of claim 3 wherein said naphthenic and aromatic oil mixture is admixed with said low asphalt content lubricating oil stock just prior to introduction of the latter into the contacting Zone.

5. In the fractionation and recovery of lubricating oil constituents from a low asphalt-content lubricating oil stock with propane wherein a hard deposit of asphalt precipitates and adheres to and plugs the oil fractionating apparatus, a process for continuously carrying out said fractionating operation Without plugging said apparatus by deposited asphalt comprising maintaining a body of liquid propane containing oil in solution in a lirst vertically disposed and elongated contacting zone, introducing said oil stock into said lirst zone at a midpoint, introducing liquid propane into said first zone at a point near the bottom thereof, withdrawing propane containing dissolved oil from the top and Withdrawing an oil-rich liquid phase containing dissolved propane and free from precipitated asphalt from the bottom oi said rst zone, separating the oil from the withdrawn propane containing dissolved oil, maintaining a body of phenol in a second elongated and vertically disposed contacting zone, introducing the separated oil into the body of phenol in said second zone at a point near the bottom thereof, introducing phenol into said second zone at a point near the top thereof, removing a raffinate phase from the top and an extract phase comprising a mixture of aromatic and naphthenic oils from the bottom of said second zone, separating said mixture of aromatic and naphthenic oils from the last mentioned extract phase, introducing the separated mixture of aromatic and naphthenic oils free from phenol into said body of propane at the point of introduction of said low asphalt content lubricating oil stock.

6. In the process of claim 5, introducing the separated mixture of aromatic and naphthenic oils free from phenol into said body of propane in the ratio of from 3 to 25 per cent by volume based on the low asphalt-content lubricating oil stock introduced into said iirst Zone.

7. In the process of claim 6, maintaining the ratio of the volume of propane to oil feed between the limits of 7:1 to 8:1 and maintaining the temperatures at the top and midpoint of said body of liquid propane at F. and 185 F., respectively, and maintaining said body of propane under a pressure of 640 pounds per square inch.

BRUCE C. BENEDICT. WILLIAM N. AIDE;

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,086,487 Bahlke et al July 6, 1937 2,198,388 Landau Apr. 223, 1940 2,202,389 Lewis et al May 28, 1940 

1. IN THE PROCESS FOR SEPARATING AND RECOVERING A LUBRICATING OIL FRACTION FROM A LOW ASPHALTCONTENT CRUDE LUBRICATING OIL STOCK WITH PROPANE WHEREIN A HARD DEPOSIT OF ASPHALT IS FORMED AND ADHERES TO AND PLUGS THE OIL FRACTIONATING APPARATUS, A METHOD FOR CONTINUOUSLY CARRYING OUT SAID FRACTIONATING OPERATION WITHOUT PLUGGING OF SAID APPARATUS BY DEPOSITED ASPHALT COMPRISING MAINTAINING A BODY OF LIQUID PROPANE IN A CONTACTING ZONE, INTRODUCING SAID OIL INTO SAID ZONE AT A MIDPOINT, INTRODUCING LIQUID PROPANE INTO SAID ZONE AT A POINT NEAR THE BOTTOM THEREOF, WITHDRAWING PROPANE CONTAINING DISSOLVED OIL FROM THE TOP AND WITHDRAWING AN OIL-RICH LIQUID PHASE FREE FROM PRECIPITATED ASPHALT FROM THE BOTTOM OF SAID ZONE; SEPARATING THE OIL FROM THEE PROPANE CONTAINING SAID DISSOLVED OIL; MAINTAINING A BODY OF PHENOL IN A SECOND CONTACTING ZONE, INTRODUCING THE SEPARATED OIL INTO SAID BODY OF PHENOL AT A POINT NEAR THE BOTTOM AND INTRODUCING PHENOL AT A POINT NEAR THE TOP THEREOF, REMOVING A RAFFINATE PHASE FROM THE TOP AND AN EXTRACT PHASE FROM THE BOTTOM OF SAID SECOND ZONE, SEPARATING A MIXTURE OF AROMATIC AND NAPHTHENIC OILS FROM SAID EXTRACT PHASE AND INTRODUCING THE SEPARATED MIXTURE OF AROMATIC AND NAPHTHENIC OILS FREE FROM PHENOL INTO SAID BODY OF PROPANE AT THE POINT OF INTRODUCTION OF SAID LOW ASPHALT-CONTENT CRUDE LUBRICATING OIL STOCK. 